The goal of this research project is to understand the nature of mouse embryonic and somatic stem cells and to identify genes that are responsible for the maintenance of cellular pluripotency. To extract the common features of stem cells, we have been conducting global gene expression profiling with the mouse embryonic cDNA microarrays developed in our laboratory. We have thus far profiled the following stem cells: (1) Differentiation and lineage commitment of pluripotent mouse embryonic stem (ES) cells. Expression profiling of mouse ES cells at six time points during the course of their differentiation has been performed. (2) Comparison between mouse ES cells and Trophoblast Stem Cells. (3) Mesenchymal stem cells and derivative osteoblast cells. (4) Neural Stem cells and neuron/glia cells. (5) Hematopoietic stem cells. We are currently working on data analysis and independent validation of results. We also plan to do expression profiling on Embryonic Germ (EG) cells, on ES cells with the altered expression of Stat3, and on ES cells with altered expression of Oct-3/4.